Present day office copy machines use papers coated with zinc oxide and doped with dyes to increase their sensitivities to optical light. In their uses, these coated papers are charged to a peak potential at a first station in the machine, and then transported to another station where they are optically exposed to the item to be copied. However, the surface potential on the paper often decreases during the time of this transport. As is understood, this decrease in potential causes a decrease in the possible contrast of the reproduced print. Additionally, some potential may remain at the surface of the paper after it is exposed to the optical light. This residue attracts toner particles and gives the print a grayish background and a further reduction in contrast.
Many different factors affect the quality of the reproduced print. For example, the specific manufacture of the zinc oxide, the manufacture of the doping dyes, the manufacture of the paper, and the process of coating the paper with the oxide and dyes -- all, in addition to the specific manufacture of the copy machine itself. Thus, investigations have shown that different qualities of print reproduction have been obtained for the same machine, but with different copy papers; and that different qualities have been obtained for the same papers, but in different copy machines. Although some suppliers of coated papers advertise a product acceptable for use in any one of many machines, results have shown a wide disparity in the quality of the print from machine to machine. Reasons for these differences include variations in the specific zinc oxide compositions manufactured, in the dye doping compositions, in the paper manufactures, in the coating processes employed -- all, with the possible result that one brand of paper, while producing quite acceptable copy at one time for a given machine, could produce quite different results at a later time. Another reason for the variation in quality is that each machine manufacturer has the option of selecting the charging potential, transport time and light exposure interval for optimum results using its own recommended brand of paper, but such parameters may not produce optimum results with papers available from other manufacturers.
As will be readily appreciated by those skilled in the art, these variations in copy reproduction result from a lack of quality control in the industry. For example, if the quality of a reproduced print from one machine is somehow inferior to a prior print, the machine user cannot accurately determine whether the difficulty is due to the internal workings of the machine, to the coating process employed, or to the characteristics of the uncoated paper, the zinc oxide, or the doping dyes -- all that he knows is that the reproduction has deteriorated. What is needed is a quality control, through the pre-testing of the coated paper to be used, to facilitate an understanding that any deterioration in reproductive qualities is due to the machine itself, and not to any external factors.